Health & Safety and Technical notes

At station B, the rod used for the torsional pendulum must be balanced. Two rods fastened together with elastic bands or a shorter length of wire may also be tried.

At station C, provide a second boss-head so that students can investigate the effect of increasing the load. The position of the boss head along the length of the metre rule could also be varied.

At station D, have students alter the water levels by blowing into the tube or use a simple puffer bottle. The water will then perform damped harmonic motion.

At station G, set up the board leaning backwards a little, at about 10° - 15°.

Procedure

At each station, displace the system from its equilibrium position and carefully observe what happens. Listen to the differences if a sound is made.

Teaching notes

1 These experiments can give students a qualitative appreciation of a range of oscillators. Encourage them to use their own initiative to develop a description (graphical or otherwise) of the motion of an oscillator in its cycle. Careful work will provide the basis for discussions about the displacement, velocity and acceleration of the oscillator. You could introduce the terms displacement, amplitude, period, frequency.

2 Features common to all harmonic oscillations are:

each complete oscillation of a system takes the same time

a force returns the system to its equilibrium position when displaced

an inertia factor makes the system overshoot its equilibrium position when in motion.

If the acceleration of a body is directly proportional to its distance from a fixed point, and is always directed towards that point, the motion is simple harmonic.

Some systems have a period of oscillation which depends on the mass. In many systems, the amplitude of oscillation decreases with time.

The link from acceleration of an oscillator to the force on the oscillator is obvious but should nonetheless be stressed as later modelling depends upon consideration of the changes in the force on an oscillator during its cycle.

3 Expected results for some of the stations:

A The periodic time, T, depends on the length, l. (The motion is isochronous.) T ∝ l½.

C This behaves like a very large ticker-timer blade.

D The motion is damped by fluid friction but is clearly isochronous. Would the period be the same if a denser liquid is used?

E Listen to the sound: what does this tell you about the motion? The amplitude decreases but the frequency remains unaltered.

F Load the end of the wig-wag with a variable number of masses so that it oscillates sideways. Note the affect of mass on the time for one oscillation.

G Listen to the sound the ball makes as it rolls or slides along the tracks. The circular track will give what sounds like an isochronous motion; the parabolic track gives a frequency that increases as the amplitude decreases; the V-shaped track is not isochronous at all.